Investigation of Modulation Schemes for Flexible Line-Rate High-Speed TDM-PON

We investigated modulation schemes for realizing flexible line-rate PON. The flexibility can be used to optimize PON resource usage. We considered cases based on experimental results taken with single carrier as well as multicarrier schemes. The multicarrier schemes provide most optimal line-rate granularity which can be somewhat traded off with their inherent reduced receiver sensitivity. Total throughput of a flexible DMT-PON using just a 10G APD/TIA outperforms flexible PONs based on single carrier dual-rate or triple-rate schemes detected with 25G APD/TIA or 33 GHz EDFA/PIN receiver normalized to 25 Gb/s sensitivity. Of the single carrier cases we investigated, the dual rate 25 Gb/s NRZ/50 Gb/s EDB (or 25 Gb/s NRZ/50 Gb/s equalized to NRZ) case also performs well with respect to obtainable overall throughput. This is due to the relatively small penalty between 25 Gb/s NRZ and 50 Gb/s EDB when compared to 25 Gb/s NRZ and 50 Gb/s PAM-4, which effectively means a smaller line-rate granularity for NRZ/EDB. To further illustrate the advantages of introducing flexibility in PON systems we calculated the throughput of a dual-rate PON based on NRZ/EDB for N1, N2, E1, and E2 class power budgets assuming just N1 rated transceivers. We show that with just a few percent throughput reduction N2-class can be supported with N1-class transceivers. And with about 20% throughput reduction a E1-class PON can be supported with N1-class transceivers.